Field of the Invention
The present disclosure relates generally to components of track-type machines, such as track chain bottom rollers, track chain links, track pin bushings, track pins and track pin bushing joints, which are made of non-carburized steel having a wear-resistant coating metallurgically bonded thereto. In particular, it relates to undercarriage assembly components and other components of track-type machines that are made of non-carburized steel and that have a wear resistant coating that is metallurgically bonded to portions of the component subject to wear, such as portions of the bottom roller, surfaces where the track chain link engages and disengages, an outside diameter surface of a track pin bushing where a drive sprocket engages and disengages the surface, an inside diameter surface of the track pin bushing, and a hinge pin bushing where two machine members are hinged together, and the outside diameter surface of the pin in the track pin bushing and the hinged pin joint.
Description of Related Art
In the discussion of the state of the art that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art against the present invention.
An endless track is a chain made up of links, track pin bushings, track pins, bottom rollers and shoes. FIG. 1 shows these undercarriage assembly components in a representative section of a track on a track-type machine, i.e., a crawler tractor. Each section of the track is a pair of links fastened together with a track pin bushing at one end and a track pin at the other end. The track pin fits inside the bushing to hold the next pair of links. Both the track pin and the track pin bushing are typically “press fit” into the links so the section does not work apart during the service life of the track. One track pin on each track, the so-called master pin, is held in by a snap ring to allow removal and separation of the track, for example, when performing repairs or maintenance of the track. A track shoe, having a desired grip or grouser determined by the environment of intended use (e.g., clay, slit, loam, gravel, snow, mud, or hard surfaces) is bolted to each section to provide traction.
The undercarriage assembly components of track-type machines, such as track chain bottom rollers, track chain links, track pin bushings, track pins and track pin bushing joints in endless tracks of a track-type machine are subjected to very severe operating environments. For example, debris, soil, rocks and so forth can enter the track and undercarriage of a track-type machine, such as a crawler tractor, during operation. These materials can subsequently accumulate between the engaging surfaces of the undercarriage assembly components and engaging surfaces of the drive equipment, pack into the area between them and/or directly grind, wear, pit, scratch or crack the surface of the undercarriage assembly components. A track that is adjusted too tight can increase friction and cause accelerated wear to undercarriage assembly components, such as track pins and track pin bushings. In an extreme case, severely tight track adjustment can cause the track to run extremely hot and “draw-back” the hardness of undercarriage assembly components, such as track pins and track pin bushings, i.e., heat treat the components resulting in a reduction in the components' hardness, and even cause the track pins and track pin bushings to fuse together. At the other end of the spectrum, a too loose track can allow drive sprocket teeth to jump links, especially in reverse, causing wear to undercarriage assembly components such as the teeth and the track pin bushings, bottom rollers, and so forth.
Undercarriage assembly components are subject to wear. For example, there are two types of wear on track pins and track pin bushings—external wear and internal wear. External wear takes place on the outer diameter of the track pin bushings in the area contacted by the drive sprocket teeth. This contact area is about ⅓ or more of the surface of the track pin bushing and occupies the majority of the center length of the track pin bushing. Wear occurs on the outside diameter of the track pin and the inside diameter of the track pin bushing. Additionally, where the track pin bushings are fitted into the track link counterbores, internal wear can occur on the outside diameter of the ends of the track pin bushings. Thus, current track pins and track pin bushings in endless tracks experience wear and stress which can negatively impact the service life of the track pin bushing.
Current track pins and track pin bushings are typically formed from materials that are hardened to decrease wear and increase service life. For example, current track pins are case hardened by carburizing the alloy and then quenching. However, these materials and methods still result in a relatively short service life. Thus, in addition to material selection for hardness and wear resistance, current track pins and track pin bushings are either turned or replaced to present a new wear surface to the sprocket and consequently extend service life. See, for example, Louis R. Hathaway, Ed., “Tires and Tracks, Fundamentals of Service”, Moline, Ill.: Deere and Company, 1986, pp. 47-67. However, the track pins and track pin bushings must be turned prior to being worn past the wear limit, or they will not be serviceable. Thus, frequent inspection and maintenance of track pins and track pin bushings occurs to identify and ameliorate components that have worn, resulting in the associated down time of equipment and personnel.
In addition, other pin/bushing (P/B) joints are widely used as hinges between two machine members in various types of machinery such as heavy equipment including tractors, construction, forestry and mining equipment. The P/B joint while serving as a hinge is also required to serve as a loaded bearing during relative motion between the two machine members connected to the joint. Such a joint, by virtue of its location on the machine and depending on the type of machine, is exposed to a dusty environment. The dust from this environment, which is mostly fine sand particles, enters into the space between the pin and the bushing and causes accelerated wear of the pin and the bushing mating surfaces and thus reduces the joint life. This then makes it necessary to replace the joint frequently even with frequent daily or weekly changing of the lubricant. The accelerated wear due to sand particles is due to the higher hardness of sand as compared to the hardness of the pin and bushing surfaces.
In conventional track/pin bushings, mating surfaces, which are the outer surface of the pin and the bore surface of the bushing, are case carburized and the parts are then quenched and tempered to obtain a high hardness on the surfaces. These high-hardness surfaces are more resistant to abrasion by fine sand particles (which travel from the outside environment into the clearance between the pin and the bushing) than if they were not carburized. This leads to a longer life of the P/B joint. However, the surface hardness obtained by this method of carburizing and quenching is only about 60-62 HRC which is much less than the hardness of the sand particles and therefore the technique provides only a limited P/B wear protection and life extension. The sand particles which enter into the clearance space between the pin and the bushing get mixed with the lubricating grease (which is injected into the clearance) and the effectiveness of the grease gradually diminishes. This makes it necessary to force out the grease from the joint clearance space frequently, sometimes daily, depending on the degree of joint seal effectiveness, and the environment in which the machine is working, to get the sand out of the joint. This frequent purging of grease helps increase the joint life to some extent. Nevertheless, this purging operation, if required to be done frequently, becomes time consuming and wasteful.
Other current undercarriage assembly components are typically formed from materials that are hardened to decrease wear and increase service life. For example, current bottom rollers are hardened by quenching. However, these materials and methods still result in a relatively short service life. The wear problem is aggravated because sand is much harder than even the hardened steel and wear of the bottom roller cannot be substantially reduced by simply hardening the contact surface. Thus, frequent inspection and maintenance of bottom rollers occurs to identify and ameliorate components that have worn, resulting in the associated down time of equipment and personnel. Similar efforts with similar limited results are known for other undercarriage assembly components.
Also, for example, undercarriage track chain links that form a part of the undercarriage assembly are subjected to severe wear and corrosion. Wear is caused by continuous contact with undercarriage rollers which themselves are hardened. The wear rate is enhanced due to abrasive action of dry sand and wet sand slurry and other hard materials such as rocks, trapped between the link and roller contact surfaces. The wear problem is further aggravated due to the fact that sand is much harder than even the hardened steel, and wear of links cannot be substantially reduced by simply hardening the contact surface. Therefore a solution other than heat treatment is required to reduce wear rate to prolong the life of the link substantially.
Also, due to the functional nature of the crawler and other construction and mining equipment, the undercarriage parts of these machines are required to be in intimate contact with wet sand and mud continuously. This causes the link surfaces to corrode, thus producing a synergistic effect on wear. This corrosion cannot be reduced by hardening the steel. Any other superficial surface treatment of links, such as carburizing, nitriding or other conventional surface treatment methods, are not cost effective against the wear- and corrosion-indicated that environment that the links face during service. A more expensive material, such as a highly alloyed steel or other advanced material, therefore does not constitute used since such a substitution would substantially increase cost and cannot be an acceptable solution.
A solution to the problem which can reduce both wear and corrosion and also which can be applied in a production environment and at a low cost, is required.
A change in the current manufacturing process of components is proposed. The current method involves hot forging medium carbon steel containing various amounts of boron, manganese, chromium and others, machining mating surface and induction hardening select surfaces.
Coating a metal surface with another metal or metal alloy to enhance appearance, protect against corrosion, or improve resistance to wear is often referred to as “hardfacing” or “hard surfacing.” For example, see Alessi U.S. Pat. No. Re. 27,851, Revankar U.S. Pat. No. 5,027,878 and U.S. Pat. No. 5,443,916, Brady, et al., U.S. Pat. No. 4,682,987, and Hill U.S. Pat. No. 5,456,323.
Hardfacing is often done by fusing a powdered, hard metal alloy onto a metal surface. In endless track applications, metal parts subject to wear can be case hardened to improve wear resistance. However, application of current wear-resistant coatings prior to carburizing results in oxidation of the wear-resistant coating during subsequent carburizing with an adverse impact on the wear-resistant properties of the coating.
Accordingly, longer wearing surfaces on undercarriage assembly components of endless tracks used in track-type machines, such as track pin bushings, are desired to extend the service life and to reduce the long-term maintenance cost associated with endless tracks. Further, a method of producing such a longer wearing surface by coating with a wear-resistant alloy while still obtaining a desired wear resistance of the uncoated portions of the component by other suitable means, i.e., case hardening, and in particular, by induction hardening is desirable.
Also, due to the functional nature of the heavy machinery construction, mining and forestry type equipment, the components, both the undercarriage assembly components and the hinge joint components, of these machines are required to be in intimate contact with wet sand and mud continuously during the machine operation. This causes components such as the bottom roller surfaces to corrode, thus producing a synergistic effect on wear due to abrasion. This corrosion cannot be reduced by hardening the steel. Any other superficial surface treatment of bottom rollers such as carburizing, nitriding or other conventional surface treatment methods are not cost effective or adequate against a highly wear- and corrosion-prone environment which the bottom rollers face during service. A more expensive material such as a highly alloyed steel or other advanced material, cannot be used since such a substitution would substantially increase cost without a corresponding increase in performance, and cannot be an acceptable solution.
A solution to the problem which can reduce both wear and corrosion and also which can be applied in a production environment and at a low cost is required.
U.S. Pat. No. 6,414,258 discloses a method of applying beads of hard material to sprocket teeth and bushings of a base carrier for a tracklaying vehicle. In this method, the beads are applied sequentially by weld overlays (an obviously slow process) and produce a sinusoidal type surface which is detrimental to the mating part such as the chain link. Because of the bead nature of the deposit, it takes a substantial time to generate a smoother surface by initial wear. Before this smooth wear surface is produced, the deposited contact surface can cause damage to the mating link surface.